import re
import tkinter
import tkinter.messagebox

root = tkinter.Tk()
#设置窗口大小和位置
root.geometry('300x270+400+100')
#不允许改变窗口大小
root.resizable(False,False)
#设置窗口标题
#root.title('简易计算器-董付国')

#放置用来显示信息的文本框，并设置为只读
contentVar=tkinter.StringVar(root,'')
content = tkinter.Entry(root,textvariable=contentVar)
content.place(x=10,y=10,width=280,height=20)

#按钮通用代码，参数btn表示按钮的是哪个按钮
def buttonClick(btn):
  content = contentVar.get()
  #如果已有内容是以小数点开头的，前面加0
  if content.startswith('.'):
    content = '0' + content

  #根据不同按钮做出相应的处理
  if btn in '0123456789':
        content += btn
  elif btn == '.':
      #如果最后一个运算数中已经有小数点，就提示错误
      lastParyt = re.split(r'\+|-|\*|/]', content)[-1]
      if '.' in lastPart:
          tkinter.messagebox.showerror('错误','小数点太多了')
          return
      else:
         content += btn
  elif btn == 'C':
      #清除整个表达式
      content = ''
  elif btn == '=':
      try:
         #对输入的表达式求值
         content = str(eval(content))
      except:
         tkinter.messagebox.showerror('错误','表达式有误')
         return
  elif btn in operators:
     if content.endswith(operators):
         tkinter.messagebox.showerror('错误','不允许存在连续运算符')
         return
     content += btn
  elif btn =='Sqrt':
     n = content.split('.')
     if all(map(lambda x:x.isdigit(),n)):
         content = eval(content)**0.5
     else:
        tkinter.messagebox.showerror('错误','表达式有误')
        return

     contentVar.set(content)
#放置清除按钮和等号按钮
btnClear = tkinter.Button(root,
                         text='Clear',
                         command=lambda:buttonClick('C'))
btnClear.place(x=40,y=40,width=80,height=20)
btnCompute = tkinter.Button(root,
                         text='=',
                         command=lambda:buttonClick('='))
btnCompute.place(x=170,y=40,width=80,height=20)
#放置10个数字，小数点和计算平方根的按钮
digits = list('0123456789.') + ['Sqrt']
index = 0
for row in range(4):
   for col in range(3):
       d = digits[index]
       index += 1
       btnDigit = tkinter.Button(root,
                           text = d,
command = lambda x=d:buttonClick(x))
       btnDigit.place(x=20+col*70,
               y=80+row*50,
                width=50,
                height=20)
#放置运算符按钮
operators = ('+','-','*','/','**','//')
for index,operator in enumerate(operators):
    btnOperator = tkinter.Button(root,
                         text=operator,
                         command=lambda x=operator:buttonClick(x))
    btnOperator.place(x=1230,y=80+index*50,width=50,height=20)

root.mainloop()